Constant impedance coaxial switch

ABSTRACT

A coaxial cable switch is disclosed which maintains a constant impedance through the switch by providing a contact configuration with the same ratio of inner conductor diameter to outer conductor diameter as is provided by the cable. The switch is operated by inserting a conductive liquid into a cavity resulting from a discontinuity in the inner conductor of the switch, thereby bridging the discontinuity.

Unite States Patent Norman Wasserman Columbus, Ohio Apr. 15, 1970 Jan.4, 1972 Bell Telephone Laboratories, Incorporated Murray Hill, BerkeleyHeights, NJ.

Inventor Appl. No. Filed Patented Assignee CONSTANT IMPEDANCE COAXIALSWITCH 8 Claims, 2 Drawing Figs.

U.S. Cl 200/182, ZOO/81.6, 200/153 S, 200/195, 200/211, 200/214 Int. ClH0111 29/28 Field of Search 200/81 .6,

[56] References Cited UNITED STATES PATENTS 2,762,881 9/1956 Brockwellet al. 200/153.18 X 3,184,693 5/1965 Lanctot ZOO/153.18 X 3,278,71310/1966 Crupen ZOO/152.9

Primary Examiner-Herman J. Hohauser Attorneys-R. J Guenther and Edwin B.Cave ABSTRACT: A coaxial cable switch is disclosed which maintains aconstant impedance through the switch by providing a contactconfiguration with the same ratio of inner conductor diameter to outerconductor diameter as is provided by the ca ble. The switch is operatedby inserting a conductive liquid into a cavity resulting from adiscontinuity in the inner conductor of the switch, thereby bridging thediscontinuity.

i/RELEASE ATE PATENTEDJRN 4:972

525ml @25 5 A l l l I I I ll INVENTOR M WASSERMAN 1 ATTORNEY CONSTANTIMPEDANCE COAXIAL SWITCH This invention relates to fluidically actuatedswitching devices and more particularly to such devices as are suitablefor use in communication switching networks, specifically networks usedfor the switching of high-frequency signals, such as radio and videofrequency signals and coaxial cable transmission lines.

Background of the Invention The communication systems widely used at thepresent time employ large numbers of switches to provide the numerousinterconnections required within the system. The desirability ofminiaturizing these switches is apparent and requires no explanation.However, miniaturization of conventional switches used to carryhigh-frequency signals in a coaxial cable introduces a problem. Sincethe conventional contact configuration is that of two overlappingblades, commonly known as the reed switch," appreciable capacitivecoupling is introduced between the contacts in an open condition whenhigh-frequency signals are present. A good example of this switchconfiguration, and an early attempt to solve the capacitive couplingproblem, is US. Pat. No. 3,355,684 issued Nov. 28, 1967 to D. S. Churchand R. W. Kordos. In addition, a relatively high contact resistance isobtained from the operated switch, and perhaps as disturbing, theresistance is of a variable nature. This necessarily affects the returnloss characteristics as well as the insertion loss.

A further serious problem results from the change in shape between thecontacts of the switch and the conductors in the coaxial cable. Sincethe impedance in coaxial cables is a function of the ratio between theinner and outer conductors, it is apparent that switches of this typewill necessarily introduce impedance variations into the transmissionsystem.

It is therefore an object of my invention to provide a switching devicewhich introduces essentially no impedance variation into thetransmission path.

It is also an object of my invention to provide a switching devicehaving very low contact resistance.

It is a further object of my invention to provide a switching devicewhich has its overall size miniaturized yet permits a large spatialseparation between the switch contacts to minimize capacitive couplingwhen the switch is in the open state.

SUMMARY OF THE INVENTION In an illustrative embodiment of my invention aswitch is provided to selectively connect two discontinuous ends of thecenter conductor of a coaxial cable. The two contacts of the switch havea circular cross section with the same diameter as that of the innerconductors of the cable. To operate the switch, a conductive liquid froma reservoir within the switch is forced into a chamber between the twoswitch contacts. Since the outside diameter of the chamber is the sameas that of the inner conductor of the cable, no impedance variations areintroduced. Also, since a large separation may be obtained between thecontacts in an open condition, and a wetted contact is obtained in aclosed condition, capacitive coupling and contact resistance areminimized in the switch.

DESCRIPTION OF THE DRAWING FIG. I is a cross-sectional view of anunoperated switch embodying my invention; and

FIG. 2 is a cross-sectional view of the device of FIG. 1, shownoperated.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT The switch shown in FIG. 1comprises contacts 101 and 107, corresponding to the inner conductor ofa coaxial cable, which are separated from each other by chamber 105.Coaxial with contact 101, and located at its inner end, is cavity 102.Contact 107 also has a coaxial cavity 108 at its inner end. This cavityis substantially larger than cavity 102 and acts as a reservoir for asupply of liquid mercury. Surrounding the contacts and chamber isdielectric I10 and outer conductor III of the coaxial cable. Cavity I02connects through a fluid port to a source of fluid actuating pulses (notshown). Reservoir I08 connects through fluid port II6 to a second sourceof fluid actuating pulses (also not shown). Ports I15 and 116 are, ofcourse, constructed from an insulating material to prevent the shortingof the inner and outer conductors. The inner diameter of ports 115 andI16 is small enough so that, due to its high surface tension, mercuryfrom reservoir 108 and cavity I02 will not enter the ports.

To operate the switch, as shown in FIG. 2, a fluid pulse is applied tothe reservoir through port 116. Mercury is forced out of cavity 108 andinto chamber 105 and cavity 102. When chamber 105 is completely filled,a wetted contact having almost zero resistance is obtained betweencontact I01 and contact 107. Since the outside diameter of chamber 105is the same as that of contacts 101 and 107 which act as innerconductors in the coaxial cable, it should be apparent to thoseunderstanding the problems of switching high-frequency signals that theimpedance of the switch is the same as that of the coaxial cable, sincethe ratio between the diameters of inner and outer conductors is thesame for both.

To release the switch assembly and return it to the condition shown inFIG. I, a fluid pulse is applied to cavity 102 through port 115. Themercury in chamber 105 is forced back into reservoir I08, interruptingthe contact established between conductors I01 and 107.

In order to minimize the capacitive coupling between conductors I01 and107, the width of chamber 105 may be made quite large. Naturally, cavity108. and the supply of mercury in the reservoir must be correspondinglyincreased. However, no matter how large chamber 105 is made, theimpedance through the switch remains unchanged since the ratio betweenthe diameters of the inner and outer conductors is unchanged. Also,increasing the size of chamber 105 has little effect on the resistanceof the switch. Since a wetted contact is obtained at both contacts, thechange in switch resistance is merely the resistance of the additionalmercury, which is effectively zero regardless of the quantity necessaryto fill chamber 105.

Although the switch described is fluidically actuated, other actuationmodes are equally applicable. For example, the switch may be gravityactuated or magnetically actuated using magnetic mercury" consisting ofa colloidal suspension of iron particles in a mercury base. Any skilleddesigner could devise a number of actuation modes and a variety ofswitch configurations without departing from the inventive principlesdisclosed. However, the switch described is probably the simplest,smallest, most economical and effective structure possible.

What I claim is:

l. A coaxial switch comprising a continuous cylindrical outer conductor,

a discontinuous cylindrical inner conductor, coaxial with the outerconductor and having a first end and a second end, wherein the length ofthe discontinuity is sufficient to prevent capacitive coupling betweenthe first and second ends when the switch is unoperated,

a reservoir of conducting liquid,

means for operating the switch by inserting liquid from the reservoirinto the discontinuity between the first and second ends of the innerconductor, thereby establishing a conducting path between the first andsecond ends, and

means for constraining the inserted liquid to impart a peripheralconfiguration thereto which is substantially the same as that of theinner conductor,

whereby the impedance of the switch is essentially equal to that of acoaxial cable of similar size since the ratio between the diameters ofthe inner and outer conductors is the same through the switch as it isthrough the cable.

2. A coaxial switch in accordance with claim I wherein the operatingmeans comprises means for applying a pressurized fluid pulse to theliquid reservoir.

3. A coaxial switch in accordance with claim I wherein the reservoir islocated within the first end of the discontinuous inner conductor.

4. A coaxial switch in accordance with claim 1 wherein the constrainingmeans comprises a dielectric sleeve between the inner and outerconductors.

5. A coaxial switch in accordance with claim 1 further including meansfor releasing the switch by evacuating the discontinuity and returningthe inserted liquid to the reservoir, thereby interrupting theconducting path between the first and second ends.

6. A coaxial switch in accordance with claim 5 wherein the releasingmeans comprises means for applying a pressurized fluid pulse to thediscontinuity.

7. A coaxial switch in accordance with claim 6 wherein the operatingmeans comprises means for applying a pressurized fluid pulse to theliquid reservoir.

8. A coaxial cable switch comprising a hollow cylindrical insulator;

an outer conductor circumscribing the insulator;

a first cylindrical inner conductor with a coaxial cavity, the

conductor filling one end of the hollow in the insulator;

a second cylindrical inner conductor with a coaxial reservoir, separatedfrom the first conductor and filling the other end of the hollow in theinsulator, wherein said separation has a length sufficient to preventcapacitive coupling between the first and second conductors when theswitch is unoperated;

conductive liquid normally contained in the reservoir;

a nonconductive fluidic conduit communicating with the reservoir fordelivering thereto a fluidic actuation pulse causing liquid from thereservoir to fill the separation between the inner conductors andestablish conductivity therebetween, the liquid being constrained by thehollow insulator so that the outer diameter thereof is equal to that ofthe inner conductors; and

a nonconductive fluidic conduit communicating with the cavity fordelivering thereto a fluidic actuation pulse causing the liquid fillingthe separation between the inner conductors to return to the reservoir,thereby interrupting the conductivity established between the innerconductors.

1. A coaxial switch comprising a continuous cylindrical outer conductor,a discontinuous cylindrical inner conductor, coaxial with the outerconductor and having a first end and a second end, wherein the length ofthe discontinuity is sufficient to prevent capacitive Coupling betweenthe first and second ends when the switch is unoperated, a reservoir ofconducting liquid, means for operating the switch by inserting liquidfrom the reservoir into the discontinuity between the first and secondends of the inner conductor, thereby establishing a conducting pathbetween the first and second ends, and means for constraining theinserted liquid to impart a peripheral configuration thereto which issubstantially the same as that of the inner conductor, whereby theimpedance of the switch is essentially equal to that of a coaxial cableof similar size since the ratio between the diameters of the inner andouter conductors is the same through the switch as it is through thecable.
 2. A coaxial switch in accordance with claim 1 wherein theoperating means comprises means for applying a pressurized fluid pulseto the liquid reservoir.
 3. A coaxial switch in accordance with claim 1wherein the reservoir is located within the first end of thediscontinuous inner conductor.
 4. A coaxial switch in accordance withclaim 1 wherein the constraining means comprises a dielectric sleevebetween the inner and outer conductors.
 5. A coaxial switch inaccordance with claim 1 further including means for releasing the switchby evacuating the discontinuity and returning the inserted liquid to thereservoir, thereby interrupting the conducting path between the firstand second ends.
 6. A coaxial switch in accordance with claim 5 whereinthe releasing means comprises means for applying a pressurized fluidpulse to the discontinuity.
 7. A coaxial switch in accordance with claim6 wherein the operating means comprises means for applying a pressurizedfluid pulse to the liquid reservoir.
 8. A coaxial cable switchcomprising a hollow cylindrical insulator; an outer conductorcircumscribing the insulator; a first cylindrical inner conductor with acoaxial cavity, the conductor filling one end of the hollow in theinsulator; a second cylindrical inner conductor with a coaxialreservoir, separated from the first conductor and filling the other endof the hollow in the insulator, wherein said separation has a lengthsufficient to prevent capacitive coupling between the first and secondconductors when the switch is unoperated; conductive liquid normallycontained in the reservoir; a nonconductive fluidic conduitcommunicating with the reservoir for delivering thereto a fluidicactuation pulse causing liquid from the reservoir to fill the separationbetween the inner conductors and establish conductivity therebetween,the liquid being constrained by the hollow insulator so that the outerdiameter thereof is equal to that of the inner conductors; and anonconductive fluidic conduit communicating with the cavity fordelivering thereto a fluidic actuation pulse causing the liquid fillingthe separation between the inner conductors to return to the reservoir,thereby interrupting the conductivity established between the innerconductors.